Laser micro-processing requires that the substrate to be processed is accurately located at the focus or image plane of an optical system. For flat sheet substrates, a flat vacuum chuck is usually used to hold the material flat and to retain it laterally to maintain registration of the part during process motion. In this case, a variety of different methods are used to achieve the required relative motion between the laser and the substrate. For small sheets, a stationary laser beam with the chuck and substrate moved in two axes is preferred for ease of laser beam delivery. For large sheets, to minimize footprint, it is common to move the laser head in two axes over a stationary substrate. This arrangement is considerably more complex in terms of beam delivery so a crossed axis approach, where the laser head moves in one axis and the substrate in the other, is also often used as a sensible compromise. In all cases a flat vacuum chuck is appropriate for retaining the substrate during processing.
Laser processing on cylindrical drum shaped substrates is very common especially in the printing industry for the production of gravure or flexographic plates. In this case, the relative motion between the substrate and the laser beam is achieved by rotary motion of the drum about its axis and linear motion of the drum or laser head in a direction parallel to the drum axis. The material to be laser processed is bonded to the drum surface so registration during processing is not an issue.
In the cases discussed above, the maximum substrate area is limited to the surface area of the flat chuck or drum. Hence, these methods are unsuitable to deal with the recent requirement from the flexible electronics industry to carry out laser process operations on devices supported on continuous webs of flexible substrate material. In this case, it is usual for the substrate material to be processed in long lengths or “webs” in so called “reel to reel” form with discrete areas of the substrate arranged along the web requiring laser patterning.
When finite lengths of substrate forming part of a continuous web of flexible material need to be laser processed, because of the limitations caused by the associated unwind and rewind drums, it is no longer possible to clamp a length of the substrate to a flat chuck and move it in two orthogonal axes. Hence, it is usual to operate in a mode where a length of the substrate is clamped to a stationary flat vacuum chuck and the laser process head is moved in two axes over the full process area by means of a motorized double gantry system. As discussed above, such an arrangement is not ideal for ease of laser beam delivery to the moving laser head.
In an associated application (GB 0806307.5), an apparatus for laser processing discrete lengths of a continuous flexible substrate is described. This apparatus uses the crossed axis approach with a flat vacuum chuck that moves in the web flow direction and a laser head that moves across the web width on a gantry. The vacuum chuck is required to move over the full length of the process area in the web flow direction so the surplus web material released at each end as the chuck moves from one end of its travel to the other is accommodated in web accumulator devices.
The length of the apparatus supporting the moving chuck is at least twice as long as the substrate process length in order to allow for movement of the flat chuck over its full length. Hence, if long sections of the web are to be processed in a single registration step, the apparatus length can become considerable. This is often inconvenient, and costly, especially if the apparatus is to be installed in a clean room, and consequently there is a requirement for apparatus that occupies less floor area yet is able to create high resolution, accurately registered, laser patterns in or on discrete lengths of flexible web materials which are unwound from reels and rewound onto reels.